An improved method of right ventricular gated equilibrium blood pool radionuclide ventriculography

Prognostic value of right ventricular ejection fraction in pulmonary arterial hypertension

Right ventricle ejection fraction (RVEF) evaluated with magnetic resonance imaging is a strong determinant of patient outcomes in pulmonary arterial hypertension. We evaluated the prognostic value of RVEF assessed with conventional planar equilibrium radionuclide angiography at baseline and change 3-6 months after initiating pulmonary arterial hypertension-specific therapy. In a prospective cohort of newly diagnosed patients with idiopathic, heritable or anorexigen-associated pulmonary arterial hypertension, RVEF was measured at baseline (n=100) and 3-6 months after initiation of therapy (n=78). After a median follow-up of 4.1 years, 41 deaths occurred, including 35 from cardiovascular causes. Patients with a (median) baseline RVEF >25% had better survival than those with a RVEF <25% using Kaplan-Meier analysis (p=0.010). RVEF at baseline was an independent predictor of all-cause and cardiovascular mortality in adjusted Cox regression model (p=0.002 and p=0.007, respectively; HR 0.93 for both). Patients with stable or increased RVEF at 3-6 months had a trend for improved all-cause survival (HR 2.43, p=0.086) and had less cardiovascular mortality (HR 3.25, p=0.034) than those in whom RVEF decreased despite therapy. RVEF assessed with conventional planar equilibrium radionuclide angiography at baseline and change in RVEF 3-6 months after therapy initiation independently predict outcomes in patients with pulmonary arterial hypertension.

Long-term outcome and effects of oral bosentan therapy in Taiwanese patients with advanced idiopathic pulmonary arterial hypertension

STUDY DESIGN

We report on the long-term outcome and effects of bosentan treatment in Taiwanese patients with advanced (functional class III or IV) idiopathic pulmonary arterial hypertension (IPAH).

MATERIALS AND METHODS

IPAH patients on stable bosentan therapy for more than 12 months and regularly monitored were eligible for this prospective uncontrolled study. Patients were evaluated for several clinical parameters, both measured at the time of initiation of bosentan therapy and after 12 months on therapy: New York Heart Association functional class (NYHA FC), change in 6-min walk distance (6MWD), right ventricle ejection fraction (RVEF), cardiothoracic ratio (CTR), and pulmonary functional status.

RESULTS

Twelve of 15 patients met eligibility requirements and were enrolled. Their mean age was 37.6+/-12.9 years and 92% were female. Six (50%) patients were in NYHA FC IV and the others were in NYHA FC III at baseline. Three (25%) patients were chronic hepatitis C virus (HCV) carriers, with normal liver function. After 12 months of bosentan treatment, 6-MWD, RVEF, and pulmonary function all increased significantly. CTR and NYHA FC both decreased significantly. Oral bosentan was well tolerated and there was no episode of liver dysfunction that required adjustment of the bosentan dosage or discontinuance of therapy.

CONCLUSION

Long-term treatment with oral bosentan appears to have beneficial effects on functional status, exercise capacity, right heart function, and pulmonary function in Taiwanese patients with advanced IPAH, regardless of whether or not they presented with chronic HCV infection.

First-pass radionuclide angiocardiography with single-crystal gamma cameras

Both multicrystal and single-crystal detectors have been in use for more than 25 years for measurement of ejection fraction by analysis of images collected during the first-pass transit of radionuclides through the heart. Originally, multicrystal cameras were preferred, because they provided higher count rates than Anger cameras; however, over the years improvements in count rate capability and collimator design have enabled Anger cameras to perform equally well. This has become an important issue now that readily available 99mTc agents, such as sestamibi, enable evaluation of both myocardial function and perfusion from a single injection. The technical abilities of a particular camera determine which acquisition protocols are most likely to provide clinically useable images for the widest spectrum of patients. Electrocardiographic-gated list mode collection is highly desirable for first-pass imaging, providing the greatest flexibility of data review, rebinning, and analysis. Attention to quality control issues of data characterization and processing is important to ensure accuracy and precision of all measurements. Accurate determinations of ejection fraction of the left ventricle are possible routinely and, under favorable circumstances, of the right ventricle as well.

Normal right ventricular systolic and diastolic function assessed by krypton-81m equilibrium ventriculography

Krypton-81m equilibrium ventriculography was used to study right ventricular function in 23 healthy male volunteers. Technetium-99m lung perfusion scintigraphy was employed to subtract radionuclide activity within lung during image analysis thereby enhancing image quality. The imaging technique was used to generate a time-activity curve for the right ventricle allowing the definition of indices of normal systolic and diastolic function for the right ventricle. At rest, indices of systolic ejection and diastolic filling were comparable to those previously reported for the left ventricle. Using the imaging technique, movement artifact during exercise reduces image quality and limits accurate measurement of these indices to resting studies.

Increased exercise capacity in hypoxemic patients after long-term oxygen therapy

Low-flow continuous oxygen can lead to significant improvement in exercise capacity in selected patients with stable hypoxemic pulmonary disease. Although the mechanisms of improvement are incompletely understood, two tenable hypotheses are (1) the relief of hypoxic pulmonary vasoconstriction and (2) improved peripheral oxygen delivery. This prospective study was performed to examine these two hypotheses. Stable patients with hypoxemic lung disease performed symptom-limited ergometry with hemodynamic monitoring before and after greater than one month of long-term home oxygen therapy. There were 22 patients who increased exercise capacity by greater than 100 KPM/min and greater than 4 min duration and 11 patients who did not increase their exercise capacity greater than 2 min or in KPM/min. Neither the responders nor the nonresponders had significant changes in pulmonary pressures or resistances or effective arterial volume elastances at exercise after long-term O2 therapy. The responders had significant increases in oxygen delivery during exercise (148 +/- 33 ml/min vs 184 +/- 51 ml/min, p = 0.004), cardiac output (7.7 +/- 1.6 L/min vs 8.7 +/- 2.1 L/min, p = 0.003), and arterial oxygen content (18.6 +/- 2.6 ml/dl vs 20.2 +/- 2.8 ml/dl, p = 0.02). The nonresponders had no significant changes in these parameters during exercise. Increased exercise capacity in response to long-term O2 therapy is associated with increased O2 delivery not relief of hypoxic vasoconstriction (in terms of pressure or resistance or arterial elastance). Increased O2 delivery can accrue from both increased cardiac output and increased arterial O2 content. Increase in arterial O2 content is unique to O2 relative to all vasodilator drugs.

Relief of right ventricular angina and increased exercise capacity with long-term oxygen therapy

Long-term low-flow oxygen therapy can lead to improved exercise capacity and improved hemodynamics in selected patients with pulmonary hypertension. We report a patient who presented with severe exercise limitation and anginal chest pain that appeared to result from pulmonary hypertension and predominantly right ventricular ischemia. Acute oxygen therapy led to relief of pain but no change in exercise capacity or of pulmonary hypertension. After eight months of oxygen therapy, the patient's pulmonary hypertension was unchanged, but right ventricular hypertrophy and marked increases in exercise cardiac output and exercise capacity developed. Thus, oxygen can relieve right ventricular angina and facilitate the development of compensatory hypertrophy.

Left and right ventricular systolic function and exercise capacity with coronary artery disease

This prospective study of symptom-limited supine ergometry was conducted to determine the contributions of right ventricular (RV) and left ventricular (LV) systolic function to the exercise capacity of a cohort of patients with coronary artery disease (CAD). Patients with unstable angina, angiographically proven CAD (n = 53) and stable symptoms after medical therapy or angioplasty were included. Documented myocardial infarction (greater than or equal to 2 weeks before exercise) was present in 43 of 53 patients. Angina was the limiting symptom in 11 of 53; the other 42 stopped exercise with dyspnea or fatigue, or both. Oxygen consumption was measured on-line during exercise with a metabolic cart. RV ejection fraction and LV ejection fraction were measured by validated methods from gated blood pool radionuclide ventriculography. There were weak but statistically significant correlations between exercise oxygen consumption and exercise RV ejection fraction (r = 0.30, p less than 0.05) and between exercise oxygen consumption and exercise LV ejection fraction (r = 0.38, p less than 0.01). Multivariate regression analysis, including exercise RV ejection fraction, exercise LV ejection fraction and exercise heart rate versus exercise oxygen consumption revealed a better relation (r = 0.48, p less than 0.005) than any variable in univariate regression. The values of RV and LV ejection fraction at rest did not correlate significantly (r = 0.2, difference not significant), but the exercise values did correlate weakly (r = 0.41, p less than 0.01). The reserve of LV ejection fraction, defined as exercise minus rest value, correlated weakly with exercise oxygen consumption (r = 0.32, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

81mKr equilibrium radionuclide ventriculography for the assessment of right heart function

Right heart 81mKr equilibrium radionuclide ventriculography was used to derive right ventricular ejection fraction (RVEF) in 12 healthy male volunteers. Anatomical lung subtraction using 99mTc-MAA perfusion scintigraphy was compared with conventional background correction and the effect of imaging projection on the techniques of image analysis evaluated. Both intra and inter observer variability were reduced by anatomical lung subtraction when compared to conventional background correction. In the right anterior oblique (RAO) projection, background corrected RVEF was lower than lung subtracted RVEF - 0.544 +/- 0.05 and 0.612 +/- 0.08 (mean +/- SD) (P less than 0.02). Lung subtracted RVEF in the anterior projection was lower than that with background correction (P less than 0.05) and lower than lung subtracted RVEF in the RAO projection (P less than 0.001). We conclude that optimal separation of right heart structures is achieved in the RAO projection and that reproducibility of the analytical technique is improved by anatomical lung subtraction.

Reduced exercise capacity of chronic obstructive pulmonary disease patients exercising with noseclip/mouthpiece

A noseclip and low resistance mouthpiece are often used to monitor exhaled gases during exercise. Because otolaryngologic studies suggest that 50% of airway resistance is in the nose and mouth, it was hypothesized that patients with advanced chronic obstructive pulmonary disease might be artifactually limited by exercise testing with a noseclip and mouthpiece. Accordingly, 12 patients with stable chronic obstructive pulmonary disease performed identical symptom-limited supine bicycle exercise tests with and without noseclip and mouthpiece. Right-sided cardiac hemodynamic measurements, radionuclide ventriculography and arterial and mixed venous gas sampling were performed during each exercise test. Exhaled gases were analyzed during the noseclip/mouthpiece exercise. The order of exercise tests was alternated. Comparing exercises with and without a noseclip, there were significant reductions in exercise duration (397 +/- 270 vs 300 +/- 230 seconds, p less than 0.01), exercise oxygen consumption (780 +/- 279 vs 638 +/- 200 ml/min, p less than 0.01) and exercise cardiac output (8.4 +/- 2.7 vs 7.3 +/- 2.0 liters/min, p less than 0.05), an increase in right ventricular ejection fraction (0.39 +/- 0.08 vs 0.43 +/- 0.08, p less than 0.01) and no change in exercise heart rate (106 +/- 14 vs 106 +/- 14), right-sided cardiac pressures or arterial and mixed venous blood gases. These data suggest that a noseclip/mouthpiece can limit exercise tolerance in advanced chronic obstructive pulmonary disease patients. This limitation may result from decreased right-sided cardiac preload (venous return).

Quantitative radionuclide angiocardiography

Quantitation of cardiac pump function using radionuclide angiocardiography provides objective information for the management of patients with heart disease. Left and right ventricular ejection fraction, stroke volume ratio, ejection rate, diastolic function, ventricular volume, parametric imaging, amplitude and phase analysis, and shunt quantification can be measured from the radionuclide angiocardiogram at rest, during exercise, and during pharmacologic interventions. This review describes these methods and discusses their reliability and their role in the clinical assessment of patients with cardiac disease.

Reproducibility of determination of right ventricular ejection fraction by radionuclide imaging: assessment by the statistical method of variance components

Confidence limits for single and repeat measurements of right ventricular ejection fraction (RVEF) were established by means of a model based on the statistical method of variance components. A total of 80 subjects (age 23 to 74 years) were examined by two radionuclide methods 1) gated first-pass (fp) technique performed in a standard 30 degrees right anterior oblique projection, and 2) multigated equilibrium imaging (muga) in an individual left anterior oblique view, applying with both methods separate end-diastolic and end-systolic ventricular regions of interest. Values obtained by fp technique were clearly higher than those measured by the muga approach, and the correlation between them was only fair: RVEFmuga = 0.48 RVEFfp + 0.13; r = 0.73; SEE = 0.08. The 95% confidence limits for a single measurement were with the fp technique: 'true' RVEF = measured RVEF +/- 6 EF-units compared to +/- 16 units with the muga method. At repeat determination within an interval of four weeks, the minimal changes in measured RVEF that were statistically significant at the 5% level were with the fp technique +/- 8 units with the same observer on both occasions and +/- 9 units with different observers. Corresponding figures with the muga method were +/- 16 and +/- 22 units, respectively. The minimal changes in a subject's 'true' RVEF necessary to produce a significant change in measured RVEF were with fp technique +/- 14 units for the same observer and +/- 17 units for different observers, compared to +/- 30 and +/- 41 units with the muga method. In conclusion, the variability with the muga approach was far greater than with the fp technique and the consequent reproducibility so poor as to preclude meaningful measurement of RVEF by the muga method.

Right ventricular dysfunction and the exercise limitation of chronic obstructive pulmonary disease

This study examined right ventricular function during exercise in patients with chronic obstructive pulmonary disease to answer the following questions: Is there a significant correlation between oxygen consumption at maximal exercise and exercise right ventricular ejection fraction? Does the right ventricular ejection fraction response to exercise correlate with exercise changes in pulmonary artery pressure, total pulmonary resistance or pulmonary vascular resistance? Which combinations of cardiac, ventilatory and blood gas variables are the best predictors of oxygen consumption at maximal exercise? Twenty-six patients with stable chronic obstructive pulmonary disease performed symptom-limited supine bicycle exercise with simultaneous hemodynamic and radionuclide ventriculographic measurements. The oxygen consumption at maximal exercise correlated with the exercise right ventricular ejection fraction (n = 21, r = 0.66; p less than 0.005), exercise stroke volume (r = 0.68; p less than 0.001), exercise cardiac output (r = 0.77; p less than 0.00005) and exercise ventilation (r = 0.85; p less than 0.00001). The change in right ventricular ejection fraction from rest to exercise correlated inversely with the change from rest to exercise in total pulmonary resistance (r = -0.51; p less than 0.05) but not with the change in mean pulmonary pressure (r = -0.37) or in pulmonary vascular resistance (r = 0.09). Multivariate analysis showed that the variables giving the highest combined correlation with oxygen consumption were ventilation and right ventricular ejection fraction (r = 0.95, adjusted r2 = 0.88). These results suggest that exercise oxygen consumption of patients with chronic obstructive pulmonary disease is related to right ventricular systolic function, exercise right ventricular dysfunction is related, in part, to abnormal exercise total pulmonary resistance, and exercise limitation in chronic obstructive pulmonary disease occurs as a result of the dynamic interaction between disordered right heart function and ventilation.

Thermodilution measurement of the right ventricular ejection fraction

This study addressed the clinical reproducibility and validity of the thermodilution (TD) measurement of the right ventricular ejection fraction (RVEF). Forty-one patients underwent right heart catheterization, including TD RVEF, within 2 h of gated first pass (GFP) and gated blood pool (GBP) radionuclide ventriculography; 21 had single plane contrast right ventricular angiography (ANGIO) during the same catheterization. Analysis of variance showed no difference among three successive TD RVEF measurements. (table; see text) Stroke volume by RV ANGIO correlated with Fick (n = 10, r = .86) and thermodilution stroke volume (n = 21, r = .88). It is concluded that although the thermodilution method is an accurate way to measure flow, it is not an accurate way to measure right ventricular ejection fraction, and by inference, ventricular volumes. The most likely explanation for this finding is incomplete mixing as in previous studies of indicator methods of measuring left ventricular volumes.

Exercise radionuclide right ventriculography in children

Supine exercise equilibrium radionuclide right ventriculography was performed in 13 children (8-18 years) with hypercholesterolemia. Phase analysis was used to construct right ventricular regions of interest, and a peri-right ventricular region was used for background correction. Right ventricular ejection fraction at rest and exercise was 50.5 +/- 9.2% and 61.5 +/- 8.1%, respectively, with a mean increase of 11.0 +/- 7.5 percentage units (range 1-27 percentage units). During exercise, end-diastolic volume remained unchanged while end-systolic volume decreased by 19.4%, producing a 21.7% increase in stroke volume. Stroke volume ratios (left ventricular stroke volume counts/right ventricular stroke volume counts) approach unity (1.00 +/- 0.27). However, interobserver and intraobserver correlations are just fair, implying only a modest degree of accuracy and reliability of the procedure. This imprecision needs to be considered when evaluating the results of nuclear equilibrium right ventriculography.

Acute oxygen in patients with sleep apnea and COPD

Nocturnal oxygen administered to patients with disordered breathing ameliorates hypoxemia. As a result, an important chemical stimulus to arousal is diminished. This could cause prolongation of disordered breathing events, worsen respiratory acidosis, and induce potentially harmful cardiac arrhythmias. The presence of chronic obstructive pulmonary disease (COPD) could further aggravate the situation since such patients may have depressed hypercarbic responses. To test this hypothesis, 20 obese men with sleep apnea and COPD were studied polysomnographically on two nights receiving air on one or oxygen at 4 L/min on the other. Supplemental oxygen increased mean DOB event duration from 25.7 to 31.4 seconds (p less than 0.001), increased end apneic PCO2 from 52.8 to 62.3 mm Hg (p less than 0.025), and decreased mean end apneic pH from 7.34 to 7.28 (p less than 0.001). At the same time, it improved mean sleeping and end-apneic oxygen saturation. The number of ventricular extra-systoles (PVCs) per minute of sleep showed small increases in three subjects while breathing oxygen. Complex ventricular arrhythmias were unaffected by oxygen in five subjects. Oxygen eliminated atrioventricular block in two subjects. We conclude that nocturnal supplemental oxygen does not increase ventricular arrhythmias in the majority of patients with COPD and coexisting disordered breathing events. While the clinical significance of an oxygen associated increase in ventricular extrasystoles in three subjects is unclear, nocturnal monitoring by telemetry or ambulatory recorder should be sufficient to detect such patients.

Right ventricular function at rest and during exercise in aortic and mitral valve disease

Right ventricular function at rest and during exercise was examined in a group of patients with symptomatic aortic or mitral valve disease, or both. The right ventricular ejection fraction was less than 45% in 22 of 36 patients at rest and in 12 of 17 subjects at symptom-limited, supine bicycle exercise. The right ventricular ejection fraction failed to increase more than 5% with exercise in 17 of 17 patients. The central venous pressure was greater than 5 mm Hg in 18 of 36 patients at rest and in 13 of 17 patients at maximal exercise. There was a significant inverse relation between rest right ventricular ejection fraction and mean pulmonary artery pressure (r = -0.47, p less than 0.05) and between rest right ventricular ejection fraction and mean central venous pressure (r = -0.39, p less than 0.05). There was no significant relation between the exercise values of these variables. In individual patients, the changes in right ventricular ejection fraction and pulmonary artery pressure with graded exercise were nonlinear. It is concluded that right ventricular function is not a simple function of pulmonary artery pressure at rest or during exercise in aortic and mitral valve disease. Less than one-quarter of the variation in right ventricular ejection fraction at rest can be explained by the variation in pulmonary artery pressure, and the finding of a normal (greater than 45%) right ventricular ejection fraction does not reliably exclude the possibility of pulmonary hypertension in a patient with valvular heart disease.

Right ventricular ejection fraction measurement: contrast ventriculography versus gated blood pool and gated first-pass radionuclide methods

Radionuclide methods of measuring the right ventricular (RV) ejection fraction (EF) provide noninvasive means of evaluating right-sided cardiac function at rest and exercise. This study compared 2 radionuclide methods with a cast-validated contrast angiographic method of RVEF analysis in 21 consecutive patients who underwent RV contrast ventriculography and gated equilibrium blood pool radionuclide ventriculography. Eleven subjects had gated first-pass radionuclide studies that were technically adequate for EF analysis. RVEF was calculated by different operators for the contrast and radionuclide methods. The close correlation of the contrast angiographic method with both equilibrium blood pool and first-pass radionuclide methods supports the use of the radionuclide techniques.

Sources of variability in the radionuclide angiographic assessment of ejection fraction: a comparison of first-pass and gated equilibrium techniques

Measurements of ejection fractions (EF) determined by first-pass and gated equilibrium radionuclide angiography are widely believed to be equivalent. To compare these measurements in a large group of patients over a wide range of EF values, left ventricular (LV) and right ventricular (RV) EFs at rest were measured in 135 consecutive patients who underwent the 2 methods of radionuclide angiography within 1 hour: first-pass upright with a multi-crystal camera in the anterior projection and gated equilibrium supine with a single-crystal camera in the left anterior oblique projection. The population included 18 normal patients and 117 patients with various cardiac and pulmonary disorders. First-pass and gated equilibrium LVEF correlated well (r = 0.83, p less than 0.001), but the slope of the regression line was different from unity, with the first-pass values lower than the gated equilibrium values (0.51 +/- 0.16 vs 0.56 +/- 0.15, p less than 0.05 [mean +/- standard deviation] ). Among the 45 patients with a gated equilibrium LVEF of less than or equal to 0.50, the correlation (r = 0.84) was better than that for the 90 patients with a LVEF greater than 0.50 (r = 0.44, p less than 0.05). However, in the latter group, the correlation remained good in the 15 patients with cardiomegaly due to aortic or mitral regurgitation (r = 0.80). Inter- and intraobserver error was similar for both methods. In contrast, there was a poor correlation between first-pass and gated equilibrium RVEF, with the first-pass values higher than the gated equilibrium values (0.51 +/- 0.11 vs 0.43 +/- 0.11, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

The acute effects of low flow oxygen and isosorbide dinitrate on left and right ventricular ejection fractions in chronic obstructive pulmonary disease

The objectives of this study were to determine the effects of low flow oxygen and isosorbide dinitrate on rest and exercise biventricular ejection fractions in patients with chronic obstructive pulmonary disease and to relate these ejection fraction responses to changes in pressure and flow. Nine patients with stable, moderate to severe chronic obstructive pulmonary disease who had no prior history of heart failure performed supine exercise with simultaneous hemodynamic and radionuclide ventriculographic monitoring. Eight patients performed a second exercise during low flow oxygen breathing and five performed a third exercise after ingesting 10 mg oral isosorbide. Oxygen led to a decrease in exercise pulmonary artery pressure in all subjects and a decline in total pulmonary resistance in five of the seven in whom it was measured. Right ventricular ejection fraction increased 0.05 or more only in subjects who had a decrease in total pulmonary resistance. Isosorbide fed to an increase in rest and exercise right and left ventricular ejection fractions with simultaneous decreases in pulmonary artery pressure, total pulmonary resistance, blood pressure and arterial oxygen tension. These results suggest that in patients with chronic obstructive pulmonary disease but without a history of right heart failure, the right ventricular systolic functional response to low flow oxygen and isosorbide at rest and exercise is, in part, determined by changes in total pulmonary resistance. The chronic relation between right ventricular ejection fraction and pulmonary hemodynamics in patients with chronic obstructive pulmonary disease remains to be evaluated.

The effect of pulmonary hypertension on systolic function of the right ventricle

This study sought to determine if the right ventricular ejection fraction (RVEF) could be used to diagnose pulmonary hypertension noninvasively. The right ventricular ejection fraction was measured with gated blood pool radionuclide ventriculography and compared to hemodynamic measurements made within 48 hours in 57 subjects. There was a significant inverse relationship between the RVEF and pulmonary artery pressure (r = .57, p less than .001) and the sensitivity of RVEF greater than .45 in diagnosing pulmonary hypertension was .76. Other significant determinants of right ventricular function, including right coronary disease, left ventricular function and tricuspid regurgitation, were also considered.

The normal right ventricular response to supine exercise

Nine normal, healthy young males performed graded, maximal supine bicycle exercise with monitoring of hemodynamic and gated blood pool parameters. Right ventricular ejection fraction (RVEF) was greater than 0.45 in all acquisitions at rest (mean +/- SD = 0.53 +/- 0.05) and increased greater than 0.05 in all subjects with maximal exercise (mean +/- SD = 0.69 +/- 0.06 at stage 4). There was a very close correspondence between RV and LV stroke counts from the radionuclide angiograms at rest and all exercise levels in all patients. Cardiac output changes by radionuclide data from the RV correlated closely with those obtained by the Fick technique. Multivariate analysis of RVEF vs pulmonary artery pressure, total pulmonary resistance, and heart rate showed that RVEF was inversely related to total pulmonary resistance in these patients (n = 43 acquisitions, r = 0.61, RVEF = 0.75 -- 0.001 TPR in dynes-sec/cm5 Sy.x = 0.07) and positively related to heart rate (n = 43, 4 = 0.78, RVEF = 0.34 + 0.0025 x HR Sy.x = 0.05). RVEF was not significantly related to the other hemodynamic parameters. These results suggest that in normal subjects RV systolic function is afterload-dependent and that total pulmonary resistance may be a suitable afterload index. The results emphasize that heart rate must be considered when comparing RVEF changes.